In accordance with certain embodiments, the present invention relates to method and apparatus for lockable inserts for oilfield equipment and, more particularly, to equipment used subsea for choke applications among others.
Offshore oilfield operation frequently requires making connections subsea, typically using Remotely Operated Vehicles (ROVs) or divers. Typically a connection between a male and female component completes the subsea connection. The connection can be a pipe coupling or the insertion of a valve interior component into a housing that is located subsea. Once the connection is brought together it is locked into that position, thus securing the connection.
The subsea environment is hostile, and issues of attack on the components over a period of time are a concern in any such connection. Another general concern is debris that can get into the area where the locking is to take place. Over time some of these effects can operate in tandem to preclude a secure locking of the connection or to prevent unlocking when it is time to undo the connection. Exposure of the actuation assembly to seawater can also undermine its effective operation. Yet another issue affecting such connections is the long term effect of transmitted vibration to the connection, which can unintentionally move the actuation mechanism that locks the locking dogs into a surrounding recess or groove and potentially cause an inadvertent separation of the connected components.
U.S. Pat. No. 6,237,964 is illustrative of the issues that are confronted in such subsea connections. With reference to the numerical reference numbers presented in this patent, Ostergaard shows a female component 14 that accepts a valve insert 4 and 6. To connect these components, an actuating sleeve 20 is movable axially as the ring gear 28 that has threads 26 engages threads 24 on sleeve 20 to urge the sleeve down behind dogs 45. The downward movement of the sleeve places dogs 45 into a locked position where surfaces 41 and 44 engage, thus locking the connection. In essence, the lower end of sleeve 20 cams the dogs 45 into locking engagement with the opposing recess in the female component 14. A seal 18 is at the same time actuated to hold the pressure within the connection when the two components are locked together.
A few features of this design are worth noting. The dogs 45 and their surrounding groove are exposed to seawater that enters between housing 11 and top face 22. The operating mechanism that moves the sleeve 20 axially up or down is also exposed to seawater where the threads for driving engage one another. Additionally, there is no backup device to unlock the connection if the sleeve 20 fails to come up with the existing drive system. Finally, there is no device in this assembly to compensate for transmitted vibration which could result in inadvertent axial motion of sleeve 20 as vibration induces rotation back to input shaft 34. In essence, the connection can inadvertently release because of vibration induced axial movement of the sleeve 20 that induce rotation at the threaded connection and back to input shaft 34.
A similar design is offered by Liaaen and shown in FIG. 1. It features a female component or valve body 10 that accepts a male component or insert 12. When the two components are pushed together, a seal 14 retains pressure within the body 10. In the split view of FIG. 1 it can be seen that the insert 12 is secured to the body 10 by the urging of the dogs 18 into an opposing recess or slot 16. An axially movable sleeve 20 then gets behind dogs 18 to prevent retraction of the dogs from recess 16. An input shaft 22 rotates a mating thread 24 with the result being that the sleeve 20 can be moved axially in opposed directions. While a housing 26 keeps the driving components for the insert 12 isolated from seawater, it is clear that the rest of the components for locking the connection are exposed to seawater via fluid pathways represented by arrow system 30. Seawater can have negative impacts on a threaded connection 24 by precluding makeup or release with no backup system available to raise sleeve 20 if rotation of shaft 22 does not get the job done, for instance. The dogs 18 are in seawater, and there is no anchoring mechanism to hold the position of sleeve 20 against vibratory forces.
Those skilled in the art will appreciate the manner in which such problems are addressed from the description of the preferred embodiment, the drawings and from the full scope of the invention in the appended claims.